The present invention relates to processes for recovering protein from agricultural commodities such as corn and, more particularly, relates to processes for recovering protein from agricultural commodities which are used for alcohol production.
The world is faced with a critical shortage of energy from conventional fuels, thus necessitating the development of alternate or supplemental fuels. However, alternate fuels must be produced as economically as possible in order to be competitive with existing fuels while simultaneously avoiding the creation of new shortages due to consumption of resources needed elsewhere.
One alternate fuel that has received a lot of attention is alcohol which is produced from food crops. Corn is the primary food crop being used in the production of fuel grade alcohol. Its use in the production of fuel alcohol has sparked controversy and concern. Opponents claim that the use of corn and other food crops to produce fuel will intensify the decline in per capita food production on a worldwide basis.
Since only sugars and starches from the corn are used in the production of alcohol, efforts have been made to recover the protein and other unused components of the grain. For example, as conventionally processed, stillage and residual spent grains which comprise roughly one third of the weight of the corn and include all of the corn protein, are used as an animal feed ingredient. Some attempts to recover food protein from fermented grains and stillage have been attempted. However, the quality and quantity of recoverable protein has been low, thus making it generally unsuitable as a food supplement for human consumption.
One process for recovering protein from stillage is set forth in Satterlee, et al., "The Chemical, Functional, and Nutritional Characterization of Protein Concentrates from Distillers' Grains," 53 Protein Concentrates 739-749 (1976). In this process, the stillage from the fermentation process was centrifuged and separated into a syrup and wet solids. The wet solids were mixed with sodium hydroxide at a pH of 12.2 to extract the protein. The alkaline extract was removed by centrifugation and was acidified to a pH of 4.0 with HCl to precipitate out the protein. The precipitate was washed with ethyl alcohol and with water and was separated by centrifugation to obtain a distillers protein concentrate. The Satterlee article also indicated that various modifications such as sonication, pretreatment with papain and pretreatment with 1% sodium sulfite could be used to effect the amount of protein recovered.
A process is disclosed by Wu, et al., "Protein Concentrate from Normal and High-Lysine Corns by Alkaline Extraction: Preparation," 41 Journal of Food Science 509-511 (1976), for recovering protein from corn before it is treated by any other process. The corn is ground in a hammer mill and the protein is extracted by a 0.1N sodium hydroxide solution in two steps. After centrifugation, the alkaline extract from each step is adjusted to a pH of 4.7 to recover the protein as a precipitate. Bran is removed from the starch and protein by screening the second alkaline dispersion, and the protein and starch are separated by centrifugation.
Essentially the same process has been used to recover proteins from sorghums. Wu, "Protein Concentrate from Normal and High-Lysine Sorghums: Preparation, Composition, and Properties," 26 J. Agric Food Chem., 305-309 (1978).
Attempts have also been made to recover protein from other corn products. For example, corn is often processed to recover starch and syrups. One of the by-products of these processes is corn gluten. Corn gluten is generally used as animal feed because of its high unsaturated fatty acid content which promotes rancidity development. A method based on fat extraction to upgrade corn gluten for use in human food is disclosed in Daley, et al., "Food Applications of a Corn Protein Concentrate," Miles Laboratories, Inc., Industrial Products Group. In this process, the wet corn gluten is extracted with a hot ethylacetate-ethanol-water azeotropic mixture. The corn protein is separated by centrifugation which is then washed by water to remove residual solvent and oligosaccharides.
While the foregoing processes provide methods for recovering proteins from corn and other types of grain, they generally do not produce food grade protein or else they are plaqued by other disadvantages. Accordingly, it would be a significant advancement in the art to provide a process for recovering food grade protein from corn and other grains wherein the remainder of the corn could be used in other processes such as alcohol production. Such a process is disclosed and claimed herein.